178. O you who believe! Al-Qisas (the Law of Equality in punishment) is prescribed for you in case of murder: the free for the free, the slave for the slave, and the female for the female. But if the killer is forgiven by the brother (or the relatives, etc.) of the killed against blood money, then adhering to it with fairness and payment of the blood money, to the heir should be made in fairness. This is an alleviation and a mercy from your Lord. So after this whoever transgresses the limits (i.e. kills the killer after taking the blood money), he shall have a painful torment.
179. And there is (a saving of) life for you in Al-Qisas (the Law of Equality in punishment), O men of understanding, that you may become Al-Muttaqun (the pious - see V.2:2).
The person who forgives has high honor in Islam. God love those who love humans. It is in the discretion of the victims of deceased to forgive the offender or not in case of murder.